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The greenhouse effect ______________________.
A.
is decreasing overtime and so is not an issue that scientists take seriously
B.
is clearly a negative phenomenon because it heats up the earth's temperature
C.
can be a positive phenomenon because it keeps the earth's temperature from being too low for life to exist, but can also be a negative phenomenon when too much greenhouse gas is stored in the atmosphere
D.
is clearly a positive phenomenon because without the greenhouse gases, the earth's temperature would be too cold for life